A flexor tendon injury affects the tendons of the anterior forearm, those on the palm side of the arm that cross the wrist joint and insert on the finger bones. The tendons are what enable the muscles to flex, or curl inward, the wrist and fingers. Injuries to these tendons include deep cuts to the wrist or hand that may sever the tendons and inflammatory repetitive stress injuries like carpal tunnel syndrome. Acute forms of flexor tendon injury like muscle strains may also affect these tendons if the wrist is bent back abruptly, as in catching oneself on one’s hands during a fall.

Located in the anterior compartment of the forearm, the flexor muscles with tendons crossing the wrist joint include the flexor carpi radialis, palmaris longus, flexor carpi ulnaris, flexor digitorum superficialis, flexor digitorum profundus, and flexor pollicis longus. There are nine flexor tendons in all, with four belonging to the flexor digitorum superficialis and one for each of the other muscles. Six of these tendons, those belonging to the flexor digitorum superficialis, flexor digitorum profundus, and flexor pollicis longus, lie deep in the wrist and pass through a space among the cluster of carpal bones in the base of the hands known as the carpal tunnel. The remaining three, those belonging to the flexor carpi radialis, palmaris longus, and flexor carpi ulnaris, are closer to the surface and cross the palm side of the wrist near the skin.

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A type of flexor tendon injury that afflicts the superficial tendons is a deep cut to the wrist. These tendons can potentially be severed, causing them to snap backward in either direction like rubberbands. As the superficial tendons attach to the hand near the wrist joint, a deep cut will result in difficulty or a complete inability to flex the wrist. A deep cut to the palm of the hand or palm-side surfaces of the fingers can similarly damage any of the deep flexor tendons that attach to the finger bones, resulting in an inability to curl the fingers. Cut tendons almost always require surgery to repair, as the detached ends pull so far apart.

Another highly common form of flexor tendon injury is carpal tunnel syndrome. A repetitive stress injury (RSI) brought on over time by frequent, repetitive, and prolonged flexing of the wrist joint, carpal tunnel can be initiated by behaviors ranging from typing on a keyboard to sleeping with the wrists curled. It is caused by inflammation of the deep flexor tendons, which swell and pinch the median nerve, a large nerve that also passes through the carpal tunnel. Symptoms include pain, numbness, and tingling in the hand that can radiate up the arm, particularly on the thumb side.

Flexor tendon injury can also result from an abrupt trauma that forcefully bends the wrist backward, straining the tendons. An example is catching oneself on one’s hands upon falling. Strains are felt as pain, stiffness, and tenderness on the inside of the wrist joint, symptoms that may be accompanied by bruising and swelling if the pull on the tendons is severe.

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